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Topic: Arduino Uno USB ground connected to ground pins (Read 288 times) previous topic - next topic

the_bear

Apr 11, 2020, 01:32 pm Last Edit: Apr 11, 2020, 07:28 pm by CrossRoads
Hello, I was wondering if it is correct if the USB port ground pin is connected directly to the all ground pins of the Uno board ?

For example, if I use the Uno board for an application and I power it through the USB port from the 5V output of a 7805 regulator and the ground of the 5V regulator is connected to ground of the USB port and to all other grounds available on the pins of the Arduino.
Please have a look at the attached schematic...

spycatcher2k

#1
Apr 11, 2020, 01:36 pm Last Edit: Apr 11, 2020, 01:36 pm by spycatcher2k
Yes - thats how grounds work!!!
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Peterd51

Hi,

quetion for the experienced contributors here...

in this set up would it be better to connect the extrernal voltage through the Vin and ground, through the DC power jack or the USB port?

Could any of these methods be likely to cause problems when supplying power in?

Thanks,
Peter

hammy

#3
Apr 11, 2020, 05:23 pm Last Edit: Apr 11, 2020, 05:25 pm by hammy
Depends ..all are equally valid options , there is no best way .

The Vin allows you to use a wider range of voltages ( see spec) . The USB is useful  for powering off your computer when you want to Program it or run it . You need around a min of 7.5v if using Vin.

Note there are power limitations in both options , you should not be using the Arduino itself to supply " significant" power to other devices.

the_bear

#4
Apr 11, 2020, 06:41 pm Last Edit: Apr 11, 2020, 06:43 pm by the_bear
Should it be a good idea to power the Arduino Uno via de 5V pin ?
I read somewhere that it is not recommended, but it is good to connect the output of an 7805 regulator directly to the 5V pin to power on the Arduino Uno ?

spycatcher2k

Quote
I read somewhere that it is not recommended
Please provide the source for this.


If you have a stable, smooth 5V source, then yes this is fine.
Mrs Drew
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CrossRoads

There are some regulators that are not happy (i.e. fail) when the output is reverse driven with 5V; their datasheet showed adding a diode from the output (anode) to the input (cathode) so that the input didn't see less than ~ 0.5 to 0.7V volts below the output.
I believe this was a problem on early Mega2560 boards when folks tried powering the board from 5V on the Power Header.  I wrote about this years ago, one can probably find it in the Old Forum (the one that is read only now).

Take a look at  the 5V regulator on your board, and look up it's datasheet to see if a diode is recommended for protection.

See Figure 13 on pages 12, 13 here  www.ti.com/lit/ds/symlink/lm1117.pdf
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

CrossRoads

#7
Apr 11, 2020, 07:48 pm Last Edit: Apr 11, 2020, 08:01 pm by CrossRoads
The diagrams in the datasheet all show Gnd from the USB connector going to the board Gnd, and with UGND and GND connected for 5V operation, with 5V coming from USB, or from the board.

I don't know the reason for the solder jumper in the Uno schematic, or if boards are delivered with the jumper soldered.

Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

the_bear

Please provide the source for this.


If you have a stable, smooth 5V source, then yes this is fine.
https://store.arduino.cc/arduino-uno-rev3

spycatcher2k

Quote
5V.This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.
This refers to supplying an unregulated voltage != 5V.
Mrs Drew
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the_bear

#10
Apr 11, 2020, 09:10 pm Last Edit: Apr 11, 2020, 09:18 pm by the_bear
I was thinking about a regulated voltage.
But if I power it from USB, then there is a fuse on the schematic (500mA), does it matter ? In other words, it is better to power the Arduino through the USB port because the fuse will protect it if something go wrong ?
Or it is better to power it through the 5V pin ?

... in terms of "phantom powering" it is better to supply the Arduino with regulated 5V through the 5V pin or through the USB port ?

spycatcher2k

If you are that worried, put a fuse in. But if you design your project well enough, you should not need it, as all you will be powering is the Arduino itself.
Mrs Drew
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sterretje

The fuse protects the power supply, not the Arduino.
If you understand an example, use it.
If you don't understand an example, don't use it.

Electronics engineer by trade, software engineer by profession. Trying to get back into electronics after 15 years absence.

the_bear

#13
Apr 11, 2020, 09:23 pm Last Edit: Apr 11, 2020, 09:24 pm by the_bear
@spycatcher2k So the recommendation is to power it via the 5V pin, with 5V regulated voltage ?

spycatcher2k

No - I gave options. The recommended way to power an Arduino is USB or 7-12 Volts on the Barrel connector.

Mrs Drew
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